Insulating material



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COATING OR Pl AST'C 8 4 Patented Mar. 11,1930

) UNITED'STATES- PATENT OFFICE :oss'rn a. cross, or swrssvats, rnnxmvaina, assumes. 'ro wns'rnwcnousn mouse a murac'ruamo courm, a conroaanou or rmmsmrvama My invention relates to insulating mate'- In addition to this pro rty, it is desirable male or med1ums and it has special relat on that the insulation s on d, in some types of to insulating coatings adapted for insulating electrical machinery, resist the action' of conwsum'rnm Jungian Application fled ll'ovember 10, m1. Serial Io. 234,503.

the core lates of transformers, dynamo-elec- 6, trio mac ines and the like.

Hitherto an organic insulating material, such as varnish or enamel, has been used for separating the sheet iron or steel plates used 1n making transformers, generators and mo- 10 tors. The insulating film or coating utilized for this work does not necessarily require a high value of specific resistance or a hi h breakdown value, but it is desirable that the insulating coating limit the contact area of 15, the sheets of iron so as to cut down eddycurrent losses. A varnish coating, however,

. is not altogether satisfactory for this purpose because it does not readily resist the effects of corona and is not effective in preventing the magnetic sheets from rusting when they are ex osed to moisture or saltwater solutions. ueh coatings are soft and easily abraded, and when pressure is ap lied to the sides of a plurality of assembled sheets which are insulated from each other in such not flow readily after application, which resists abrasion, rusting of the sheets, and the efiects of corona, and which is less expensive and less dangerous to make and use.

The improved insulating material need not have a hlgh s ecific resistance and high dielectric break own value but such properties are desirable. The material must adhere strongly1 to the surface of the sheet iron, must cover t e surface well and must resist abra- W sive action, thereby the contact area.

rona discharge. Further, the material must be such as to revent side slip 'ing of the dies 65 a used in punc in the sheets, t us preventing excessive wear 0 the dies. The material must be low in cost and easy to prepare and apply.

After considerable investigation and testing, I have discovered thata water solutionof sodium silicate is very desirable as a corep a 1n edium. I prefer to utilize a solution of specific gravity between 1.15 and 1.3.

Such coreplate insulating material, however, may be greatly improved by the addition of certain carboh drate com ounds and filler materials, sln y or in com natioxi.

fiyof'the carbo (ydrate compounds, such extrin may be used inas su r, starch or div1 ua y or in combinat on as an addition to the sodium silicate. These materials aid greatly in reventing side sli ping of the dies utilized in shearing the p ates, and the insulating compound so formed does not flow 7 readily and is not easily abraded. I prefer to use sugar because of its low cost.

' Some steel plates, such as high-grade electrical sheet steel, are customarily annealed after a plication of the insulating medium. Since t e annealing temperature is above the melting point of sodium silicate, the steel sheets would adhere to one another after removal from the bakinfizovens, i'f so'dium silicate alone was used. y using a com and comprisin sodium silicate and .a car hydrate, suc adherin of'the plates after annealing is avoid These carbohydrate compounds, on heating, break down into carbon, water and a very small Kercentage of hydrocarbons, which materials ave very little effect in increasing the carbon content of the steel plates at annealing temperature.

Although various proportions of sodium silicate, water and sugar may be used, I have found that a composition comprising substantially 60 parts of water 45 parts of sodium silicate and 10 pm war is very satisfactdry.

I may add or filler such as talc silica, clays, mica, magnesia mica and 'nnprove the electrical an mec amca ar- 5 acteristics and produce a film that will not flow under pressure. A suitable dye may also be added bto improive the co or.1 Th3 sheet steel may espraye ,painted or in the sodium silicate solution or the sod i fi m silicate may be applied by the same special machines known to the art which are used in applying varnish.

The usual process of baking is to place the sheets on a moving platform or conveyor which carries them through a baking oven. The baking process takes. about twenty five seconds. The source of heat is at the back of the oven so that a uniform raising of the temperature of the sheets to between 120 to 150 C. is secured, and it' is found that this heat treatment results in the best product.

The sodium-silicate coating may be made slightly thinner than the varnish coating or film secured in the same manner, and the specific resistance of the sodium silicate will be found to be greater than that of the varnish film. The sodium-silicate film has been found to resist the action of salt spra for a longer period of time than a varnis film.

A corona discharge for 60 hours had no appreciable effect on the sodium silicate film.

Although I have described a specific coating material and a specific use for the material, it is apparent that modifications and other uses may occur to those skilled in the art, and such modifications and uses are intended to be included within the spirit and scope of my invention,'as defined in the appended claims.

I claim as my invention:

1. An article of manufacture comprising magnetic sheet material provided with a thin, adherent, electrical insulating and heat resisting coating, said coating containing sodium silicate and a substantial proportion of finely divided mica.

2. A magnetic core for electrical devices comprising a plurality or laminations of magnetic material, the laminations being provided with thin films of adherent insulating material comprising sodium silicate, said insulating material containing a finely divided mineral insulation, and being capable of withstanding pressure.

3. An article of manufacture comprising magnetic sheet material coated with an insu lating film comprising a soluble silicate.

4. An article of manufacture comprising magnetic sheet material coated with an insulating film comprising a soluble silicate and 5. An article of manufacture comprising ma etic sheet material coated with an insulati g film comprising sodium silicate.

6. An article of manufacture comprising magnetic sheet material coated with an insu 9. The method of producing an insulatin film upon a layer of sheet material whic comprise coating the sheet material with a composition of matter comprising an aqueous solution of sodium silicate and heating the coated sheet to evaporate the water.

10. The method of roducing an insulating-film upon a layer 0? sheet material which comprises coating the sheet material with a composition of matter comprising an aqueous of sodium silicate and heating the coated sheets at a temperature between 120 and 150 C. to eliminate the water and bake the film.

11. The method of roducing an insulating film upon a layer 0? sheet material which comprises coating the sheet material with a composition of matter comprising an aqueous solution of sodium silicate and an inorganic filler and heating the coated sheets at an elevated tern erature to eliminate the water and bake the 1m. I

12. The method of producing an insulating film upon a pluralit of annealed sheets of magnetic material w ich comprises coating the individual sheets with a composition of matter comgrisin water, sodium silicate and a carbohy rate, iaking the film on each sheet to eliminate the water, assembling a pluralit of such sheets and annealing them at a su cientlg high temperature to decompose the carbo ydrate, said carbohydrate being added to the composition to prevent the sheets from adhering together during the annealing operation.

. 13. The method of producing an insulatmg film upon a pluralit of annealed sheets of magnet1c material w ich comprises coating the individual sheets with a composition of matter comprising water, sodium silicate and sugar, baking the film on each sheet to eliminate the water, assembling a plurality of such sheets and annealing them at a sufiiciently hi h temperature to'decompose the sugar, sai sugar being added to the composition to revent the sheets from adhering to ether uring the annealing operation.

11 testimony whereof, I have hereunto subscribed 1927.

- JOSEPH E. GROSS.

my name this 16th day of November, 

